The CBC, or complete blood count, measures the number of red blood cells, white blood cells and platelets in the blood. The test panel also measures a person's hemoglobin and hematocrit levels. Someone with HIV may have a higher-than-normal number of white blood cells. This is because white blood cells fight infections.

If someone with abnormal CBC results is also at risk for HIV, a doctor will order the HIV ELISA test. This test helps determine if there are HIV antibodies in the patient's blood or urine sample. If the HIV ELISA test is positive, the patient has to have the HIV Western blot test to confirm the positive result.